Wednesday, July 08, 2009

"The biggest concern is that this barrier will break small populations of animals into even smaller pieces that will result in fewer animals interacting," said Clinton Epps, a wildlife biologist at Oregon State University and co-author on the study. "A major barrier such as this could lead to significant degradation of connectivity for many different species, ultimately threatening their populations."

In their study, the authors looked at the potential effects of the security wall on two species – the pygmy owl and bighorn sheep – primarily because they already had studied those animals in that region. They found that the low-flying pygmy owl made three-fourths of its flights below the height of the security wall, which is approximately four meters high, and that juvenile owls had lower colonization in areas of disturbance or areas with less vegetation.

"Connectivity" is important for keeping wildlife populations healthy. Many species migrate from one part of their range to another to take advantage of seasonal foraging opportunities, and some move from day to day. Connectivity is also important for maintaining genetic diversity. If two parts of a population are separated by a physical barrier, they will no longer be able to interbreed. For small populations, this could risk inbreeding.

The authors suggest alterations to the wall to reduce the risk to wildlife.

"Some of the potential damage to pygmy owls could be mitigated with a few tweaks to the system," Epps added. "Putting in poles near the fence could allow the owls to swoop down from a perch, and planting brush to provide better cover could help them avoid predation by larger avian species and improve their chances for colonization."

Maintaining or augmenting trees that are taller than the fence, and that are associated with patches of dense, low vegetation should not only promote permeability, agreed lead author Aaron D. Flesch, a biologist from the University of Arizona – they may be critical. "Movement of pygmy owls from Mexico to Arizona may be necessary for the persistence of the Arizona population," Flesch pointed out.

There is also a possible solution for bighorn sheep, which are linked genetically across the Arizona-Mexico border.

"The key is to have gaps in the fence that are sufficient to allow passage of animals, while at the same time meeting security needs," Epps said. "A 'virtual' fence could be an alternative to a solid wall in some places, especially in steep terrain that is ideally suited for bighorn sheep. The use of cameras, radar, satellite monitoring and vehicle barriers could provide security and be great alternatives for wildlife."

Bighorn sheep and pygmy owls are the only species covered by the study, but they are not the only species of concern on the US-Mexican border. All of them have their own habitat and connectivity needs, so each will require varying degrees of mitigation. There is also a separate issue of urban-centered walls pushing immigrants (and their pursuers) into wilderness areas, which has its own effects on the wildlife that lives there. Of course, all of these could have been addressed at the outset if a proper environmental review had been done.